Add the changelog entry for the panel chrome change

changelog.d/1466-panel-chrome-consistency.md

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+- Give the side panels one look. Every panel title now uses the command dock's
+  label type in a brighter colour, collapsed or open; a panel lights up with a
+  blue edge and an accent title on hover, as the dock does; and every collapse
+  button sits the same distance from its panel's edge (asturksever, #1466).